The disclosed embodiments generally relate to the design of touch screens for computing devices. More specifically, the disclosed embodiments relate to the design of a power management system that provides power for a touch-enabled display.
Many types of input devices are presently used in computing systems, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and can perform one or more actions based on the touch.
One challenge in designing touch screens is that the circuitry which displays images generally operates at a different voltage than the significantly more-sensitive circuitry that senses the touches. To deal with this problem, touch-enabled displays typically cycle between a “display mode,” wherein the system operates at a corresponding display-mode voltage, and a “touch mode” wherein the system operates at a touch-mode voltage. However, it is challenging to design a power delivery system that can switch between these voltage levels quickly and efficiently.